Bacterial protein mimics its host to disable a key enzyme

Helicobacter pylori infects up to 90 percent of people in the developing world and causes gastric ulcers and cancers of the gut. Now scientists have revealed a subterfuge used by the bacterium to trick stomach cells into playing along. By injecting a protein into the stomach lining that mimics a native protein but has its opposite effect, the bacterium shuts down a process that helps properly structure stomach tissue, scientists say.

C. Erec Stebbins, head of the Laboratory of Structural Microbiology at Rockefeller University, Research Associate Dragana Nesic and colleagues deciphered the atomic structure of an important segment of the large H. pylori protein CagA as it attached to a human enzyme called MARK2. MARK2 (also known as PAR1b) regulates processes including the “tight junctions” that form between cells, packing stomach tissue together. Using the technique of x-ray crystallography, the researchers captured CagA bound to MARK2 and established the position of each atom surrounding the interaction by interpreting the pattern of x-rays diffracting from a crystallized structure of the union. The team, including biomedical fellow Marshall Miller and Brian T. Chait’s Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, published the experiments December 6 in Nature Structural & Molecular Biology. “It was the first time anyone has ever imaged CagA interacting with a human protein,” Stebbins says. “We know CagA basically shuts down MARK2, disrupting different cell functions, and we wanted to find out how that happens. We start with structure and move on to function.”